This invention relates to a wood-derived liquid smoke impregnated fibrous cellulosic casing article which is peelable from the encased foodstuff processed therein, a method for manufacturing the casing article, and a process for preparing encased foodstuffs using the casing article.
Liquid smoke may be an aqueous solution of natural wood smoke constituents prepared by burning a wood, for example hickory or maple, and capturing the natural smoke constituents in water. Alternatively, the liquid smoke may be derived from the destructive distillation of wood, that is, the breakdown or cracking of the wood fibers into various compounds which are distilled out of the wood char residue. For purposes of this invention, liquid smoke from both types of processes will be characterized as "wood-derived", and used in the aqueous form. Wood-derived aqueous liquid smokes are generally very acidic, usually having a pH as low as 2, and a total acid content of at least 3%.
Such liquid smokes may be used to impregnate the inner or outer wall of cellulosic food casings, and then transfer smoke color and/or flavor to food stuffed in the casing during processing at elevated temperatures. During this processing, the active constituents of the impregnated liquid smoke impart color and flavor to the encased food, as for example described in U.S. Pat. No. 4,377,187 to Chui in connection with fibrous cellulosic casings. By reference, Patent '187 is incorporated herein to the extent pertinent.
The as-marketed or "as-is" liquid smoke contains wood tars derived from polymerized hydrocarbons, and this tar is generally in the soluble form. However, when the as-is highly acidic liquid smoke is impregnated in the inner or outer surface of gel stock cellulosic food casings, it tends to form a tarry deposit on the carrier and squeeze rolls of the smoke treatment unit, thereby eventually forcing shutdown of the treating system. To obviate this problem, various methods have been developed to remove tar from the as-is liquid smoke before the liquid is impregnated in the cellulosic casing wall. As for example described in U.S. Pat. No. 4,592,918 to Chiu (incorporated herein by reference to the extent pertinent), these methods include at least partially neutralizing the liquid smoke to raise the pH above about 4 to form a tar-enriched fraction and a tar-depleted fraction which are separated so that the latter becomes a tar-depleted aqueous liquid smoke. The temperature is preferably maintained below about 40.degree. C. during this neutralization to partially avoid diminishment of liquid smoke staining power and/or absorptive power. Another method of tar depletion is by contacting the tar-containing liquid smoke with an organic liquid solvent under extraction conditions to form a tar-enriched liquid solvent fraction and a tar-depleted liquid smoke fraction. The fractions are separated and the latter is recovered as a tar-depleted aqueous liquid smoke.
The tubular cellulosic casings may be either small diameter, i.e. below about 40 mm., or larger diameter which is generally in the range of between about 40 mm. and about 160 mm. These casings may have fibrous e.g. paper reinforcement in the casing wall to provide dimensional stability, and most large diameter cellulosic casings are the fibrous type. Liquid smoke, like other liquid coatings, may be applied to the fibrous cellulosic casing wall by any of several methods described in the patent literature. For example, U.S. Pat. No. 3,451,827 describes a spraying method for applying a variety of coating materials over the casing internal surface. In U.S. Pat. No. 3,378,379 to Shiner et al, a "slugging" method is described for applying coating materials to the casing internal surface.
In the preparation and use of fibrous cellulosic food casings, the moisture content of the casings is of considerable importance. By way of non-limiting illustration, the casings may be shirred, i.e. compressed into a tightly compacted and pleated "stick" form by the casing manufacturer. The food processor secures a deshirred end of the casing end to the stuffing apparatus and fills the opened casing. To facilitate shirring operations on these casings without damaging them, it is generally necessary that they have a relatively low water content, usually in the range of from about 11% to about 17% by weight of total casing (16 to 28 by weight of dry cellulose), a moisture content which is relatively low compared to the moisture content required when the casing is used for food stuffing. To permit shirred fibrous casing to be stuffed without breaking of the casing during the stuffing operation, shirred fibrous casings having an average moisture content of between about 17% to about 35% of total casing weight (28% to 65% by weight dry cellulose) are required. As used hereinafter, the expression "moisture content" refers to the weight percent of water or moisture in the casing based on the weight of dry cellulose in the casing article unless another basis is specifically indicated.
Even if the fibrous casings are to be supplied in the flattened or reeled form for stuffing, they are quite stiff in the dry stock form and must have a relatively high moisture content to be sufficiently soft for stuffing without casing damage. For many years this was accomplished by soaking in water just prior to stuffing, usually for about one hour, resulting in full moisture saturation to about 150% dry cellulose (60% by weight of the total casing). With the advent of automatic high speed, high pressure stuffing equipment for products employing fibrous cellulosic casing and the need for greater control of the encased food manufacturing method for example to achieve more uniform food product, the "no soak" system was developed. This involves premoisturization of the casing prior to shirring and/or stuffing so that the fibrous cellulosic casing contains the needed moisture for stuffing without soaking. Typically a premoisturized fibrous cellulosic casing contains between about 25% and about 65% water.
Another important constituent in liquid smoke-impregnated premoisturized fibrous cellulosic casing articles is a peeling aid or "easy-peel" constituent. In particular, agents for improving the peelability of the fibrous casings from encased food products after elevated temperature processing are commonly employed. Such peelability enhancing agents include (but are not limited to) carboxymethyl cellulose and other water soluble cellulose ethers as for example described in U.S. Pat. No. 3,898,348 to Chiu et al. Another commonly used peeling aid is "Aquapel", a Hercules, Inc. trademarked product comprising alkyl ketene dimers as for example described in U.S. Pat. No. 3,905,397 to Chiu, the disclosure of which is incorporated by reference. Still another widely used peeling aid for fibrous cellulosic casings is "Quilon", an E. I. DuPont trademarked product comprising fatty acid chromyl chlorides, as for example described in U.S. Pat. No. 2,901,358 to Underwood.
Since the peeling aid must be in direct contact with the casing surface for maximum effectiveness, the prior art has preferred to apply the liquid smoke as a superimposed second coating to an already existing peeling aid coating on the casing internal surface. The resulting article may comprise a no-soak type fibrous casing article with a first Aquapel or Quilon--type peeling aid coating on the casing inner surface and a low pH as-is liquid smoke coating such as Charsol C-12 or Hickory Super Smoke superimposed on and impregnated into the first peeling aid coating. This article typically with a 32% moisture content (dry cellulose basis) has been commercially used with the SHIRMATIC 600A stuffing system (manufactured and marketed by Viskase Corporation) for producing sliced meat products as for example bologna. The article is supplied in shirred form as a stick comprising about 175-200 feet of flat casing, and used in this system to produce encased unprocessed food product at high speed. This article and the SHIRMATIC 600A system are described in copending application Ser. No. 929,455 filed Nov. 12, 1986 in the name of A. P. Urbutis. In brief, the shirred stick is deshirred, inflated and progressively drawn over an internally positioned plastic disc for transverse stretching and sizing at the rate of about 60 ft/minute. The resulting encased but unprocessed food product is gathered and clipped at the upstream end, and cut into sections of stuffed length, e.g. about 3-6 feet.
Notwithstanding the continuous frictional contact between the liquid smoke coating of the casing article and the leading surface of the plastic sizing disc, a tar coating does not appear on the disc leading surface during this commercial operation. On hindsight and based on the problem faced and overcome by the present invention, this is probably in part because each sizing disc is only used with one casing stick of about 175 ft. length, and then discarded.
Tar containing liquid smoke is manufactured by the controlled partial oxidation of wood to form vapor containing coloring and flavoring constituents and tar, with recovery of this vapor as condensate in water, and is classified by its total acid content. As will be explained hereinafter in detail, total acid content is a qualitative measure of the absorptive or staining power of the as-manufactured liquid smoke. When impregnated in cellulosic casings, higher total acid content liquid smokes generally provide more flavoring and darker colored casings and darker encased food product surface than lower total acid content liquid smokes.
During the manufacture of wood-derived liquid smoke, the total acid content is monitored and increases as more smoke vapor is recovered as condensate. In addition to increasing total acid content, the concentration of tar-like components also increases. This undesirable aspect of high acid content-stronger flavoring and darker coloring liquid smokes is due to the tar's increased solubility in lower pH--higher acidity environments. This relationship is illustrated in FIG. 1.
With wood-derived liquid smokes of less than about 6% acid content having tar contents less than about 3 wt.%, dilution with water results in a stable solution maintaining its clarity. However, for liquid smokes having higher acid content and thus higher tar content, water dilution causes soluble tars to precipitate. This is because, as the pH is raised from the initially low value of the highly acidic as-is smoke, the acid environment is altered. The tar solubility is decreased and the tars precipitate from the solution until a stable solubility level is reached. Referring to FIG. 1, the curve indicates this tar solubility limit for aqueous liquid smokes of various acid contents. A mixture on the left side of the curve will precipitate additional tar and a mixture on the right side of the curve is stable.
The aforedescribed immiscibility of high acid content liquid smokes with water is referred to as "shocking" by those skilled in the art. When the wood-derived liquid smoke is shocked with water dilution, it becomes a milky color. Soon the tar droplets coalesce and precipitate.
In certain types of food stuffing apparatus as for example the Futaba "Reel Pak" ham stuffer, there is repeated frictional contact between the unreeled fibrous cellulosic casing inner and outer surfaces and certain apparatus component(s). As illustrated in FIG. 2, a longitudinally moving shuttle is positioned within the opened casing in preparation for stuffing the ham inside the casing, and also to move the casing to the stuffing position. Each reel of fibrous cellulosic casing is on the order of 1000-1500 feet or more long, so that the shuttle and the rollers, clamps and other machine surface between the shuttle and the reeled casing supply are in repeated frictional contact with a long length of casing. For example, based on an eight hour shift and a production rate of 8 hams/minute, the Futaba shuttle contacts about 6,000 to 8,000 feet of fibrous cellulosic casing inner and outer surfaces. In contrast, each sizing disc in the aforedescribed SHIRMATIC 600A shirred stick casing article is implanted in the deshirred casing end and only contacts about 175-200 feet of casing inner surface in its particular stick and is then discarded.
Another difference between the Futaba and SHIRMATIC 600A type stuffing systems is that the fibrous cellulosic casing is subject to more physical abuse in the Futaba, i.e., more distortion in the form of bending and stretching. As a result, the Futaba system requires a more plasticized casing to withstand this distortion. In particular, it has been determined that to avoid physical damage and for high speed production, fibrous cellulosic casing must have about 8% more moisture (BD cellulose basis) for Futaba stuffing than SHIRMATIC 600A stuffing. On the other hand, excessive moisture should be avoided to minimize surface moisture and seepage from the core which would cause handling problems. This means that a fibrous cellulosic casing moisture content between about 40% and about 65% is required for stuffing in equipment of this type wherein the casing is exposed to extreme abuse and excessive tension. A preferred balance of this characteristic is a moisture content between about 45% and about 55% bone dry cellulose.
For certain end uses, the liquid smoke impregnated fibrous cellulosic casing must have the ability to impart a relatively dark color and/or strong smoke flavor to the encased foodstuff, i.e. the casing must have an absorptive index of at least about 0.4 at 340 nm. wave length. On the other hand, for stuffing without damage, i.e. breakage, the fibrous cellulosic casing must be strong in the machine direction and stretchable in the transverse direction, and this requires a relatively high water content, as previously explained. Also, for the convenience of the food processor, the moisture required for stuffing is preferably included by the casing manufacture as a "no soak" type so that processor need not further moisturize before stuffing.
There is a conflict between these requirements, because the water content of the high acid liquid smokes required for the impregnation to realize the desired absorptive index is not sufficient to simultaneously provide the fibrous cellulosic casing with the required moisture content. For example, using as-purchased ("as-is") "Charsol C-12" liquid smoke with a 12% total acid content, to obtain an absorptive index of 0.4 in fibrous cellulosic casing, 12 mg/in.sup.2 of the liquid smoke are required for slugging to achieve the desired impregnated coating on the casing inner surface. The moisture content of the resulting liquid smoke impregnated casing will be about 24 wt.% H.sub.2 O (BD cellulose)--substantially below the 40 wt.% H.sub.2 O lower limit required for stuffing without casing damage.
It is, of course, possible to use more than one liquid smoke impregnation treatment but this is inefficient and expensive. Also, two or more smoke treatments introduce additional problems because each of the as-purchased liquid smokes has a particular ratio of active smoke constituents and water, and is difficult to achieve a different ratio of active smoke constitutents: water which is required in the smoke-impregnated casing.
For these reasons, it is preferred to manufacture liquid smoke impregnated fibrous cellulose casings by first introducing the liquid smoke quantity required for the desired absorptive index, and then further moisturizing the liquid smoke impregnated casing to the required water content. However, when this is done the tar solubility limit is exceeded and tar particles precipitate within the smoke coating and the cellulose wall, for reasons explained in connection with FIG. 1. As a result, the further moisturized liquid smoke impregnated fibrous cellulosic casing is characterized by high levels of smoke and precipitated tar components on its internal surfaces. As will be demonstrated in the Examples, this occurs when the liquid smoke is the as-purchased type with its full tar content, and also to a lesser extent when tars are partially removed to provide a tar-depleted liquid smoke as the impregnating liquid. It will also be demonstrated that the same phenomenon occurs when before impregnation in the casing wall, the as-purchased low pH soluble tar-containing liquid smoke is contacted with base for neutralization and in situ tar precipitation, and further addition of base to increase the pH for resolubilization of tar.
However, it will further be demonstrated that the precipitated tars derived from the as-purchased liquid smoke and the tar-depleted liquid smoke are distinctly different from the precipitated tars derived from the high pH resolubilized tar-containing liquid smoke. This difference (based on distribution of atomic mass units as measured by a mass spectrometer) is an important aspect of the invention.
A Quilon C peeling aid first coating--Hickory Super Smoke second coating, fibrous cellulosic casing article was commercially used in reel form with a Futaba apparatus of the FIG. 2 type to stuff hams. After liquid smoke impregnation in the casing inner surface, the article was further moisturized to about 52% water (BD cellulose). In this commercial operation there was a substantial accumulation of tar on the shuttle and other upstream components of the Futaba type apparatus after only 30 minutes operation and consumption of about 450 feet of casing. Since the casing used in the Futaba system is prestuck for release of air during stuffing, there are openings through the casing wall portion permitting tar migration to the casing outer surface and accumulation on the machine parts contacting this surface. When enough tar accumulated on the guide rollers, clamps and other machine components as well as the shuttle, the tar started to come off in patches and cover the casing in spots, tending to make the ham blotchy or covered with dark spots. The food processor regarded the problem as sufficiently important to require shut down for cleaning the shuttle and other surfaces to avoid eventual binding of the casing.
An object of the present invention is to provide a fibrous cellulosic casing article with a first peeling aid coating on its inner surface and a second wood derived liquid smoke coating over the first peeling aid coating, which provides a casing absorptive index of at least 0.4 for transfer of smoke color and flavor to encased food, the casing having sufficient moisture to provide stretch flexibility during stuffing without breakage and without causing tar accumulation on "repeated frictional contact" between the liquid smoke coating and the stuffing apparatus part(s) which contact the inside and outside surfaces of the casing.
Another object is to provide an efficient method for manufacturing the aforedescribed casing article which does not require multiple liquid smoke impregnation steps.
Still another object is to provide a process for preparing encased foodstuffs such as ham, using the aforedescribed casing article and without experiencing the tar accumulation problem on the stuffing apparatus parts even though these parts and the liquid smoke coating have repeated frictional contact during the process.
Other objects and advantages of the invention will be apparent from the ensuing disclosure and appended claims.
As used herein "repeated frictional contact" means that at least 450 linear feet of liquid smoke coating on the fibrous cellulosic casing inner and/or outer surfaces, or the equivalent thereof, is in moving rubbing contact with at least one part of the stuffing apparatus. This rubbing contact may be continuous and unidirectional, so that only 450 feet of casing are required. Alternatively, the rubbing contact may intermittent and unidirectional, so that more than 450 feet of casing are required. As a further variation, the rubbing contact may be bidirectional (i.e. in opposite directions) and if continuous, only 225 feet of casing are required.
Although repeated frictional contact will be specifically described herein in connection with the Futaba type system wherein the casing is drawn from a reel in flat form, repeated frictional contact may also occur in certain types of food stuffing systems in which the casing is supplied in the shirred stick form. For example, the T-Sizer system marketed by Teepak, Inc. employs a sizing disk which is a permanent part of the machine (unlike the SHIRMATIC 600A system). Repeated frictional contact occurs in the T-Sizer system when multiple sticks having a combined flat length of at least 450 feet are consecutively contacted with the same machine-mounted sizing disk. This general type of stuffing apparatus with permanently mounted sizing means is described in U.S. Pat. No. 4,558,488 to Martinek.